Mine roof support and method of providing same



J. E. MUNN Oct. 31,1967

MINE ROOF SUPPORT AND METHOD OF PROVIDING SAME Filed June 5, 1964 INVENTOR. JOHN E.MUNN

his ATTORNEY United States Patent 3,349,567 MINE ROQF SUPPORT AND METHOD GF PROVIDING SAME John E. Munn, 704 Cascade Road, Forest Hills Borough, Pa. 15521 Filed June 3, 1964, Ser. No. 372,245 4'Claims. (CI. 61-45) This invention relates to mine roof supports and to a method for providing the same, and more particularly the invention is for a mine roof support to replace roof bolts such as those commonly used.

In many underground tunneling operations, and particularly in mining of coal and other minerals, it is the practice to at least partially support the mine roof by drilling upwardly into the roof, inserting a bolt with an expansion nut into the bore, and by turning the head of the bolt expand the nut against the wall of the bore to effectually resist downward pressure of the rock or slate formation forming the roof of the seam or strata being excavated. These roof bolts, which are ordinarily left in the mine, are relatively expensive and considerable labor is involved in the application of each one to assure that it is firmly set.

According to the present invention a length of metal tubing is used in the bore in place of a bolt. After the tubing is inserted in the bore, a proble-like instrument having a coil of known form is entered into the tube. This coil is connected in a circuit which includes a source of current, capacitors capable of storing large. amounts of energy, and a switch. Upon closing of the switch a surge of current through the coil creates enormous forces in the surrounding metal tube, bulging it outward against and even into the strata about the bore. This process of expanding metal is not new per se and is known as pulsed magnetic metal forming, but not in the environment of this invention. I

An object of the present invention is to provide a method for supporting mine roofs utilizing metal tubing in place of bolts and expanding. the tubing in situ by pulsed magnetic metal forming.

A further object of the present invention is to provide a mine roof support and method of providing the same which is cheaper, safer and easier to install than bolts with expansion nuts generally provided for this purpose.

These and other objects and advantages are secured by this invention as will be more readily apparent to those skilled in the art from the following description in conjunction with the accompanying drawings, in which:

FIG. 1 is a more or less schematic view showing the manner of setting the tubing in the bore with the coil inside the tubing ready to expand the tubing, the view being a vertical section, the tubing with the coil being shown in elevation;

FIG. 2 is a similar view showing the roof support fully completed with the coil removed;

FIG. 3 is a view similar to FIG. 2 showing the tube provided with a coupling to indicate that it may be in sections where the distance between the floor and roof does not permit of a single long tube being inserted; and

FIG. 4 is a schematic sectional view through a mine showing several supports at spaced distances and of different lengths, since this may be desirable under some conditions.

Referring first to FIG. 1, 2 designates a mine having a roof 3 into which is bored a hole 4 of suitable diameter. Slidably fitted into the hole is metal tube 5 which may be ordinary iron or steel pipe, or which may be copperlined. At the lower end of the tube is a roof plate 6 which may be welded to the tube or retained by a flange or nut. When the tube has been inserted in the bore, a probe 7 3,349,567 Patented Oct. 31, 1967 which carries two conductors supporting a coil 8 such as is now used in pulsed magnetic metal forming is projected up into it, as shown in FIG. 1. The coil is connected through its conductors and a flexible cable 9 to a portable unit 10 containing the usual electrical apparatus including large capacity electrical condensers employed in pulsed magnetic metal forming, which apparatus is well known in the art. This apparatus is connected to a source of power through a trailing cable 11 such as is commonly employed in mobile mine equipment. A manually operated switch is indicated at 12.

With the probe inserted in the bore, the switch 12 is operated to send a surge of current through the coil, the efl'ect of which is to expand the tube with great force into the surrounding earth or rock formation.

A single bulge so formed will provide great holding power, but if desired, the probe may be lowered a few inches and a second bulge formed. This is desirable because with the upper end of the tube anchored by the first bulge, the expanding of the metal a second time tends to create tension pulling the roof plate firmly against the roof. Depending on roof conditions, additional bulges may be formed, in which case the tube is set initially with the roof plate out of contact with the roof to enable the tube to contract without overstressing the tube or the roof plate.

In FIG. 2 there is shown the tube after it has been expanded three times, the expanded sections being indicated at 13, 14 and 15, but a fewer or greater number may be employed.

If the seam is low and the supports cannot be inserted in one piece, the tube may be inserted in sections as shown in FIG. 3, with couplings at 16. All other parts are the same and corresponding reference numerals have been used.

The expanded tubes are placed at spaced locations in the roof, as are usual roof bolts. As shown in FIG. 4 they may be of different lengths so that some may penetrate deeper into the roof, and the bulges may be at different levels in neighboring supports so that the shock of expanding the metal in the holes will be staggered.

The tubes are relatively cheap as compared with roof bolts with expanding anchors which are now used, and the operation of setting the supports does not require the time and labor presently involved with roof bolts, resulting in important economy to the mine operator.

It will be understood that I have shown and described very simple roof supports, but the invention is applicable also where the supports are used to hold a beam or timbering against the roof. By forming several bulges along the length of the tube, the rock formation is engaged at several places instead of being concentrated at one point, as with an expanding wedge, so that each support may sustain greater loads with safety.

I claim:

1. The method of providing a roof support in a mine which comprises drilling a hole into the mine roof, inserting a metal tube open at its lower end into the hole with its end extending below the roof into which the tube is entered and with a roof-supporting element secure-d to the exterior of its lower end, inserting a probe-like structure with a magnetic pulsation deforming coil thereon into the tube, said probe having lead wires for conducting current to the coil at its lower end, bulging a portion of the length of the tube into the earth formation in which the hole is made by magnetic pulsation through the application of electrical current to said coil, and thereafter withdrgwing the probe and its coil from the interior of the tu e.

2. The method of providing a mine roof support as defined in claim 1 wherein the tube is first expanded near its upper end to anchor it and then expanded again lower down in its length to distribute the anchoring engage- 3 ment of the tube with the walls of the bore into diflerent levels in the roof formation.

3. The method of providing a mine roof support as defined in claim 1 wherein the expansion of the tube effects a shortening of the length of the tube and draw the supporting element under tension against the roof of the mine.

4. The method of anchoring a metal support in a rocklike formation which comprises drilling a hole into the formation, inserting a metal tube open at its lower end into the hole of a diameter to fit closely within the hole, inserting a magnetic pulsating coil and a supporting probe through which current is supplied to the coil into the tube through its lower open end and then expanding the tube at intervals along its length by magnetic pulsing by moving the coil successively to different positions inside the tube for effecting each pulsation.

References Cited UNITED STATES PATENTS 2,667,037 1/1954 Thomas et a1. 2,976,907 3/ 1961 Harvey et a1. 3,148,577 9/1964 Parsons.

DAVID J. WILLIAMOWSKY, Primary Examiner.

JACOB SHAPIRO, Examiner. 

1. THE METHOD OF PROVIDING A ROOF SUPPORT IN A MINE WHICH COMPRISES DRILLING A HOLE INTO THE MINE ROOF, INSERTING A METAL TUBE OPEN AT ITS LOWER END INTO THE HOLE WITH ITS END EXTENDING BELOW THE ROOF INTO WHICH THE TUBE IS ENTERED AND WITH A ROOF-SUPPORTING ELEMENT SECURED TO THE EXTERIOR OF ITS LOWER END, INSERTING A PROBE-LIKE STRUCTURE WITH A MAGNETIC PULSATION DEFORMING COIL THEREON INTO THE TUBE, SAID PROBE HAVING LEAD WIRES FOR CONDUCTING CURRENT OF THE COIL AT ITS LOWER END, BULGING A PORTION OF THE LENGTH OF THE TUBE INTO THE EARTH FORMATION IN WHICH THE HOLE IS MADE BY MAGNETIC PULSATION THROUGH THE APPLICATION OF ELECTRICAL CURRENT TO SAID COIL, AND THEREAFTER WITHDRAWING THE PROBE AND ITS COIL FROM THE INTERIOR OF THE TUBE. 